Polycrystalline diamond

ABSTRACT

An object is to provide polycrystalline diamond applicable to diverse applications; and a water jet orifice, a stylus for gravure printing, a scriber, a diamond cutting tool, and a scribing wheel that include such polycrystalline diamond. This object is achieved by polycrystalline diamond obtained by converting and sintering non-diamond carbon under an ultrahigh pressure and at a high temperature without addition of a sintering aid or a catalyst, wherein sintered diamond grains constituting the polycrystalline diamond have an average grain diameter of more than 50 nm and less than 2500 nm and a purity of 99% or more, and the diamond has a D90 grain diameter of (average grain diameter+average grain diameter×0.9) or less.

TECHNICAL FIELD

The present invention relates to polycrystalline diamond obtained byconverting and sintering non-diamond carbon without addition of asintering aid or a catalyst.

BACKGROUND ART

Natural and artificial monocrystalline diamonds have been used forvarious applications because of their excellent properties. A toolincluding monocrystalline diamond is, for example, a water jet orifice(Patent Document 1), a stylus for gravure printing (Patent Documents 2and 3), a scriber (Patent Document 4), a diamond cutting tool (PatentDocuments 5 and 6), or a scribing wheel (Patent Document 7).

However, such monocrystalline diamond also has a property that abrasionlosses vary (uneven wear) depending on crystal orientations of thediamond. For example, abrasion loss considerably varies between the(111) plane and the (100) plane. For this reason, monocrystallinediamond applied to such tools described above is worn away only in aspecific plane in a short time as the tools are used, and predeterminedeffects are not provided, which has been a problem.

Monocrystalline diamond also has a property of cleaving along the (111)plane. For this reason, when monocrystalline diamond is applied to atool subjected to a stress during use, the tool breaks or cracks, whichalso has been a problem.

To deal with the property of uneven wear and the cleaving property ofmonocrystalline diamond, sintered diamond may be used. Such sintereddiamond is obtained by sintering diamond grains with a metal binder suchas cobalt and hence the metal binder is present among the diamondgrains. The metal binder region is softer than the diamond grains andhence is worn away in a short time. As the amount of the binderdecreases, the diamond grains come off and the effects are not providedwith stability for a long period of time. There is also a problem inthat adhesive wear occurs between the metal binder region and a metalmaterial being worked and working for a long period of time cannot beperformed.

To solve such a problem caused by a metal binder, a binderless sintereddiamond may be produced by dissolving the metal binder with acid tothereby remove the metal binder. However, removal of a metal binderreduces the binding power of diamond grains, which most likely increasesabrasion loss.

For polycrystalline diamond free from a metal binder, there is apolycrystalline diamond obtained by chemical-vapor deposition (CVD).However, this polycrystalline diamond has a small binding strength amonggrains and hence suffers from large abrasion loss, which has been aproblem.

Hereinafter, the above-described tools are specifically described.

A water jet orifice including monocrystalline diamond has a problem inthat a target cutting width is no longer achieved after the lapse ofusage time.

This is caused by the following mechanism. In such an orifice composedof monocrystalline diamond, diamond crystals in the interior surface ofan orifice bore have various crystal orientations toward surroundings.The orifice having the shape of a cylinder at the initial stage of usesuffers from abrasion in a plane susceptible to abrasion in a shorttime. As a result, the cylindrical shape of the orifice is lost and theinterior surface is expanded into the shape of a polygon such ashexagon.

To deal with such deformation into a polygonal shape caused by unevenwear, sintered diamond may be used (Patent Document 8). However, thiscauses coming off of diamond grains with a decrease in the amount of abinder as described above and an orifice bore is expanded. Thus, acutting width is not provided with stability for a long period of time,which is a problem. In particular, a water jet intended to provideenhanced cutting efficiency is configured to expel liquid containingwater and rigid particles (alumina or the like) at a high pressure. As aresult, a metal binder region, which is softer than diamond grains,wears away in a short time and a cutting width is not provided withstability for a long period of time, which is a problem.

To cover the interior surface of an orifice with polycrystalline diamondfree from a metal binder, a method may be used in which the interiorsurface of a metal orifice bore is coated with a diamond thin film freefrom a metal binder by CVD (chemical-vapor deposition) as describedabove (see Patent Document 9). However, such a diamond thin film has ashort wear life, and has a small binding strength among grains and hencehas a short wear life, which has been a problem.

Another example is a stylus for gravure printing in which natural orartificial monocrystalline diamond is used as material for the stylus(see Patent Documents 2 and 3). However, possibly because such diamondhas a property of cleaving, such a tool breaks or cracks by a stressduring use, which is a problem. Due to the property of uneven wear, suchdiamond is worn away only in a specific plane in a short time as thetool is used, and hence working for a long period of time cannot beperformed, which has also been a problem.

Still another example is a scriber including monocrystalline diamond.For example, as shown in Patent Document 4, polyhedron-shapedmonocrystalline diamond is used to scribe monocrystalline substrates,glass substrates, and the like with a vertex of the polyhedron, thevertex serving as a blade. Such a scriber composed of monocrystallinediamond is produced by working monocrystalline diamond such that the(111) plane, which is the most resistant to abrasion against a workpiecethat is to be scribed and is composed of a monocrystalline material suchas sapphire, is particularly positioned to be aligned parallel to thework to be scribed.

However, possibly because monocrystalline diamond has a property ofcleaving along the (111) plane as described above, scribers composed ofmonocrystalline diamond crack or wear unevenly when a plane used forscribing only slightly deviates from the (111) plane, which has been aproblem.

Still another example is a diamond cutting tool in which natural orartificial monocrystalline diamond is used as material for the tool (seePatent Documents 5 and 6). However, because of the problems of thecleaving property and the property of uneven wear of monocrystallinediamond as described above, such a tool composed of monocrystallinediamond has a problem in that the tool breaks or cracks due to a stressduring use, is worn away only in a specific plane in a short time as thetool is used, and working for a long period of time cannot be performed.

Still another example is a scribing wheel in which monocrystallinediamond is used as material for the scribing wheel. For example, asshown in Patent Document 7, scribed lines are formed in a brittlematerial such as glass for liquid crystal panels with the V-shaped edgeof the wheel, the edge serving as a cutting edge.

However, as with other tools, such a scribing wheel breaks or cracks dueto a stress during use because of the problem of the cleaving propertyof monocrystalline diamond, which has been a problem.

Due to the property of uneven wear, such a tool is worn away only in aspecific plane in a short time as the tool is used, and use of the toolfor a long period of time is not possible, which has been a problem. Ascribing wheel composed of monocrystalline diamond has a V-shaped edgein which crystals have various crystal orientations in thecircumferential direction. Thus, the edge having the shape of a perfectcircle at the initial stage of use is worn away in a plane susceptibleto wear in a short time and the perfect circular shape is deformed intothe shape of a polygon. As a result, the wheel becomes no longer able toroll, which has been a problem.

To deal with the cleaving property and the property of uneven wear inthe above-described various tools, a sintered diamond compact may beused as material for such tools, the compact containing metal serving asa binder (Patent Documents 7 and 10).

However, even though sintered diamond is used, the following problemsare likely to occur: a metal binder region containing cobalt or the likeis softer than diamond grains and hence wears away in a short time, andadhesive wear occurs between the metal binder region and a metalmaterial being worked such as copper and working for a long period oftime cannot be performed. Such a metal binder in the sintered diamondcompact may be removed by dissolving the metal binder with acid.However, this reduces the binding power of diamond grains, which mostlikely increases abrasion loss.

Polycrystalline diamond that is produced by CVD and is free from a metalbinder has a small binding strength among grains and hence probably hasa problem in that such diamond has a short wear life.

[Patent Document 1] Japanese Unexamined Patent Application PublicationNo. 2000-061897

[Patent Document 2] Japanese Unexamined Patent Application PublicationNo. 2006-123137

[Patent Document 3] Japanese Unexamined Patent Application PublicationNo. 2006-518699

[Patent Document 4] Japanese Unexamined Patent Application PublicationNo. 2005-289703

[Patent Document 5] Japanese Unexamined Patent Application PublicationNo. 2004-181591

[Patent Document 6] Japanese Unexamined Patent Application PublicationNo. 2003-025118

[Patent Document 7] Japanese Unexamined Patent Application PublicationNo. 2007-031200

[Patent Document 8] Japanese Unexamined Patent Application PublicationNo. 10-270407

[Patent Document 9] Japanese Unexamined Patent Application PublicationNo. 2006-159348

[Patent Document 10] International Publication No. 2003/051784

DISCLOSURE OF INVENTION Problems To Be Solved By the Invention

In view of the problems described above, an object of the presentinvention is to provide a polycrystalline diamond applicable to diverseapplications; and a water jet orifice, a stylus for gravure printing, ascriber, a diamond cutting tool, and a scribing wheel that include sucha polycrystalline diamond.

In particular, an object of the present invention is to provide a waterjet orifice that provides a cutting width with stability for a longperiod of time, a stylus for gravure printing, a scriber, a diamondcutting tool, and a scribing wheel that enable stable working for a longperiod of time, compared with conventional tools includingmonocrystalline diamonds and sintered diamond compacts containing metalbinders.

Means For Solving the Problems

To solve the above-described problems, the inventors of the presentinvention have performed thorough studies. As a result, they have foundthat a polycrystalline diamond is advantageously applicable to diverseapplications, the polycrystalline diamond not containing a metal bindersuch as cobalt, having an average grain diameter of more than 50 nm andless than 2500 nm and a purity of 99% or more, and the D90 graindiameter of the sinter being (average grain diameter+0.9×average graindiameter) or less. Thus, they have accomplished the present invention.

Specifically, the present invention is directed to, as described below,a polycrystalline diamond; a water jet orifice, a stylus for gravureprinting, a scriber, a diamond cutting tool, and a scribing wheel thatinclude such a polycrystalline diamond and allow stable working for along period of time.

<Polycrystalline Diamond>

-   (1) Polycrystalline diamond obtained by converting and sintering    non-diamond carbon under an ultrahigh pressure and at a high    temperature without addition of a sintering aid or a catalyst,    wherein sintered diamond grains constituting the polycrystalline    diamond have an average grain diameter of more than 50 nm and less    than 2500 nm and a purity of 99% or more, and the diamond has a D90    grain diameter of (average grain diameter+average grain    diameter×0.9) or less.-   (2) The polycrystalline diamond according to (1) above, wherein the    sintered diamond grains have a D90 grain diameter of (average grain    diameter+average grain diameter×0.7) or less.-   (3) The polycrystalline diamond according to (1) above, wherein the    sintered diamond grains have a D90 grain diameter of (average grain    diameter+average grain diameter×0.5) or less.-   (4) The polycrystalline diamond according to any one of (1) to (3)    above, wherein the polycrystalline diamond has a hardness of 100 GPa    or more.-   (5) The polycrystalline diamond according to any one of (1) to (4)    above, wherein the non-diamond carbon is a carbon material having a    graphite-type layer structure.

<Water Jet Orifice>

-   (6) A water jet orifice including the polycrystalline diamond    according to any one of (1) to (5) above.-   (7) The water jet orifice according to (6) above, wherein an    interior surface of an orifice bore through which water jet fluid    passes, the bore being formed in the polycrystalline diamond, has a    surface roughness Ra of 300 nm or less.-   (8) The water jet orifice according to (6) or (7) above, wherein the    orifice bore formed in the polycrystalline diamond has a diameter of    10 μm or more and 500 μm or less.-   (9) The water jet orifice according to any one of (6) to (8) above,    wherein a ratio (L/D) of an orifice level (L) to an orifice bore    diameter (D) is 10 to 500, the orifice bore being formed in the    polycrystalline diamond.-   (10) The water jet orifice according to (6) or (7) above, wherein    the orifice bore formed in the polycrystalline diamond has a    diameter of more than 500 μm and 5000 μm or less.-   (11) The water jet orifice according to any one of (6), (7),    and (10) above, wherein a ratio (L/D) of an orifice level (L) to an    orifice bore diameter (D) is 0.2 to 10, the orifice bore being    formed in the polycrystalline diamond.

<Stylus for Gravure Printing>

-   (12) A stylus for gravure printing including the polycrystalline    diamond according to any one of (1) to (5) above.

<Scriber>

-   (13) A scriber including the polycrystalline diamond according to    any one of (1) to (5) above.-   (14) The scriber according to (13) above, wherein a cutting face at    a tip of the scriber has a shape of a polygon including three or    more edges and the edges, in part or entirety, of the polygon are    used as a blade.

<Diamond Cutting Tool>

-   (15) A diamond cutting tool including the polycrystalline diamond    according to any one of (1) to (5) above.

<Scribing Wheel>

-   (16) A scribing wheel including the polycrystalline diamond    according to any one of (1) to (5) above.

Advantages

Polycrystalline diamond according to the present invention does not wearunevenly and hence is applicable to diverse applications.

A water jet orifice according to the present invention can provide acutting width with stability for a long period of time, compared withconventional orifices including monocrystalline diamonds and sintereddiamond compacts containing metal binders.

A stylus for gravure printing, a scriber, a diamond cutting tool, and ascribing wheel according to the present invention allow stable workingfor a long period of time, compared with conventional tools includingmonocrystalline diamonds and sintered diamond compacts containing metalbinders.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, polycrystalline diamond according to the present inventionis described in detail.

Polycrystalline diamond according to the present invention issubstantially a single-phase diamond (purity of 99% or more) and doesnot contain a metal binder such as cobalt. Such polycrystalline diamondcan be obtained by directly converting and simultaneously sinteringnon-diamond carbon serving as a material such as graphite, glassycarbon, or amorphous carbon into diamond under an ultrahigh pressure andat a high temperature (temperature: 1800° C. to 2600° C., pressure: 12to 25 GPa) without a catalyst or a solvent. The resultantpolycrystalline diamond does not wear unevenly, which does occur inmonocrystals.

Note that a method is known by which polycrystalline diamond is producedfrom diamond powder or graphite serving as a material. Specifically,methods by which polycrystalline diamonds are produced from diamondpowder serving as a material and polycrystalline diamonds obtained bythese methods are disclosed in References 1 to 4 below.

[Reference 1] Japanese Unexamined Patent Application Publication No.2006-007677

[Reference 2] Japanese Unexamined Patent Application Publication No.2002-187775

[Reference 3] Japanese Patent No. 3855029

[Reference 4] Japanese Unexamined Patent Application Publication No.2004-168554

Reference 1 discloses a polycrystalline diamond and the diamond grainsconstituting this polycrystalline diamond have an average grain diameterof 80 nm to 1 μm, which is in the range defined by the presentinvention. However, Ref 1 states that the polycrystalline diamond wasobtained by the method described in Ref 2. Reference 2 states thatpolycrystalline diamond is produced by a method of sintering diamondpowder with carbonate serving as a sintering aid and the carbonateremains in the resultant polycrystalline diamond after the sintering.Therefore, the structure of the polycrystalline diamond disclosed in Ref1 is different from the structure of a polycrystalline diamond accordingto the present invention.

Another method of sintering diamond powder with a sintering aid isdisclosed in Ref 3. However, Ref 3 states that it has been ascertainedwith IR spectra that the sintering aid partially remains in apolycrystalline diamond obtained by this method. Therefore, thestructure of this polycrystalline diamond is also different from thestructure of a polycrystalline diamond according to the presentinvention. Reference 4 states that the sinters of Refs. 2 and 3 areinferior in hardness to a sinter free from a sintering aid according tothe present invention. Thus, Ref 4 shows that a sinter according to thepresent invention is excellent.

Reference 4 above also discloses a method for producing apolycrystalline diamond in which a sintering aid is not used. Thismethod uses diamond micro powder as a starting material and the graindiameter of the resultant sinter is 100 nm or less, which is in therange defined by the present invention. However, non-diamond carbon isused as a starting material in the present invention. In particular,when a carbon material having a graphite-type layer structure is used asa starting material, a polycrystalline diamond can be provided having aspecial structure referred to as a lamellar structure, which is notpresent in the polycrystalline diamond of Ref 4. Reference 5 describedbelow states that extension of cracks is suppressed in a region havingthe lamellar structure. This demonstrates that a polycrystalline diamondaccording to the present invention is less prone to breaking than thatdescribed in Ref 4.

In summary, polycrystalline diamond according to the present inventionis totally different in structure from diamond sinters that have beendisclosed and, as a result, has mechanical characteristics that are farsuperior to those of the latter.

The following are examples of references describing methods of obtainingpolycrystalline diamonds in which a non-diamond carbon material servingas a starting material is converted and sintered without addition of asintering aid or a catalyst at an ultrahigh pressure of 12 GPa or moreand at a high temperature of 2200° C. or more, as in the presentinvention.

[Reference 5] SEI Technical Review, 165 (2004) 68 (Sumiya et al.)

[Reference 6] Japanese Unexamined Patent Application Publication No.2007-22888

[Reference 7] Japanese Unexamined Patent Application Publication No.2003-292397

Various tools were produced from diamonds obtained by the methodsdescribed in Refs. 5 to 7 above and the performance of the resultanttools was evaluated. Probably because the diamond described in Ref 5contains abnormally grown grains having a diameter of about 10 times theaverage grain diameter and the diamond described in Ref 6 containscoarse diamond grains that are converted from an added coarse material,the evaluation revealed that portions having such coarse grains wearextremely rapidly.

Then, thorough studies on how to eliminate such portions wearingextremely rapidly were performed and it has been revealed that thediameter distribution of sintered grains constituting polycrystallinediamond needs to be controlled. Accordingly, various tools produced withgrain diameter distributions being controlled had no grains wearingextremely rapidly and exhibited stable performance for a long period oftime. The diamond described in Ref 7 has abnormal grain growth probablybecause its production method is similar to that in Ref 5. The diamonddescribed in Ref 7 also has a problem similar to that in Ref 5.

The above-described problem can be solved by use of a polycrystallinediamond in which sintered grains constituting the polycrystallinediamond have an average grain diameter of more than 50 nm and less than2500 nm and a purity of 99% or more, and the sinter has a D90 graindiameter of (average grain diameter+0.9×average grain diameter) or less.This is because abnormal wear is suppressed by making the D90 graindiameter of sintered grains of polycrystalline diamond be (average graindiameter+0.9×average grain diameter) or less.

The average grain diameter in the present invention is number-averagegrain diameter determined with a transmission electron microscope (TEM).The average grain diameter and the D90 grain diameter can be controlledby controlling the grain diameter of a starting material or sinteringconditions.

The following are specific values for the average grain diameter and theD90 grain diameter that satisfy the above-described relationship inpolycrystalline diamond.

Example 1: when the average grain diameter is 60 nm, the D90 graindiameter is 114 nm or less.

Example 2: when the average grain diameter is 100 nm, the D90 graindiameter is 190 nm or less.

Example 3: when the average grain diameter is 500 nm, the D90 graindiameter is 950 nm or less.

The D90 grain diameter is more preferably (average graindiameter+0.7×average grain diameter) or less, and still more preferably(average grain diameter+0.5×average grain diameter) or less.

When the average grain diameter is 50 nm or less or 2500 nm or more, thehardness becomes less than 100 GPa and wearing away is caused in a shortperiod of time and hence a cutting width is not obtained with stabilityfor a long period of time.

Hereinafter, a water jet orifice according to the present invention willbe described in detail.

Since the material of an orifice according to the present invention isthe above-described polycrystalline diamond according to the presentinvention, a water jet orifice according to the present invention doesnot wear unevenly, which does occur in orifices composed ofmonocrystals.

The inventors of the present invention produced orifices with diamondsobtained by the methods described in Refs. 5 to 7 above and determinedthe cutting widths of these orifices. This determination revealed that,the diamonds obtained in accordance with these References contain coarsegrains as described above and hence portions corresponding to suchcoarse grains wear extremely rapidly. In this case, the velocity of flowof a water jet solvent decreases in such portions and the direction ofthe flow changes. As a result, the cutting width decreases or increaseswith the passage of cutting time and the cutting width is notstabilized, and hence a desired cutting width is not provided, which hasbeen a problem.

The inventors have found that, to obtain a desired cutting width withstability, such portions wearing extremely rapidly need to beeliminated, and this is achieved by controlling the distribution of thegrain diameters of a sinter. Specifically, grains wearing extremelyrapidly are eliminated in an orifice composed of a diamond having acontrolled distribution of grain diameters, the diamond beingpolycrystalline diamond according to the present invention in which thepolycrystalline diamond has an average grain diameter of more than 50 nmand less than 2500 nm and a purity of 99% or more, and the sinter has aD90 grain diameter of (average grain diameter+0.9×average graindiameter) or less. Thus, the above-described problem has been solvedwith such an orifice and use of such an orifice can provide a desiredcutting width with stability for a long period of time.

Polycrystalline diamond used for a water jet orifice according to thepresent invention preferably has an average grain diameter and a D90grain diameter that respectively satisfy the above-described ranges.

The D90 grain diameter of a sinter is desirably selected in accordancewith the average diameter of rigid particles contained in fluid used forwater jetting. When the average diameter of rigid particles issubstantially equal to or less than the average grain diameter of thestructure of a sinter, a cutting width with stability is not providedfor a long period of time. This is because rigid particles collide withnot a plurality of but a single surface of a grain of a sinter uponcollision with the structure of the sinter, and when the surface has acrystal orientation susceptible to wear, the grain wears extremelyrapidly. For this reason, the D90 grain diameter of a sinter of anorifice is selected so as to be 1/10 or less of the diameter of rigidparticles.

This is shown by the following example with specific values.

Example 4: when the diameter of rigid particles is 50 μm, the D90 is 5μm or less.

Polycrystalline diamond constituting a water jet orifice preferably hasa hardness of 100 GPa or more. When the polycrystalline diamond has ahardness of less than 100 GPa, the orifice has a shorter life.

The interior surface of an orifice bore through which water jet fluidpasses preferably has a surface roughness Ra of 300 nm or less. When thesurface roughness Ra is more than 300 nm, the orifice has a shorterlife.

When an orifice bore formed in polycrystalline diamond has a diameter of10 μm or more and 500 μm or less, the ratio (L/D) of an orifice level(L) to an orifice bore diameter (D) is preferably 10 to 500.

When an orifice bore formed in polycrystalline diamond has a diameter ofmore than 500 μm and 5000 μm or less, the ratio (L/D) of an orificelevel (L) to an orifice bore diameter (D) is preferably 0.2 to 10.

Hereinafter, a stylus for gravure printing according to the presentinvention will be described in detail.

Since the material of a stylus for gravure printing according to thepresent invention is the above-described polycrystalline diamondaccording to the present invention, a stylus for gravure printingaccording to the present invention does not wear unevenly, which doesoccur in styluses composed of monocrystals.

The inventors of the present invention produced styluses with diamondsobtained by the methods described in Refs. 5 to 7 above and inspectedthe workability of these styluses. This inspection revealed that, thediamonds obtained by the methods described in these References containcoarse grains as described above and hence portions corresponding tosuch coarse grains wear extremely rapidly. In this case, such portionscause streaky scratches on metal being worked and hence a desiredworking is not possible, which has been a problem.

The inventors have found that, to allow a desired stable working, suchportions wearing extremely rapidly needs to be eliminated, and this isachieved by controlling the distribution of the grain diameters of asinter. Accordingly, a stylus including polycrystalline diamond having acontrolled distribution of grain diameters according to the presentinvention was produced. Grains wearing extremely rapidly are eliminatedin this stylus and a desired stable working was achieved with the stylusfor a long period of time.

Polycrystalline diamond according to the present invention includessintered diamond grains having a D90 grain diameter of (average graindiameter+0.9×average grain diameter) or less. As a result, abnormalwearing can be suppressed.

Polycrystalline diamond constituting a stylus for gravure printingpreferably has a hardness of 100 GPa or more. When the polycrystallinediamond has a hardness of less than 100 GPa, the stylus has a shorterlife. When the average grain diameter is 50 nm or less or 2500 nm ormore, the hardness becomes less than 100 GPa and wearing away is causedin a short period of time and hence stable working is not possible for along period of time.

Hereinafter, a scriber according to the present invention will bedescribed in detail.

Since the material of a scriber according to the present invention isthe above-described polycrystalline diamond according to the presentinvention, a stylus for gravure printing according to the presentinvention does not wear unevenly, which does occur in styluses composedof monocrystals.

Reference 1 above discloses a scriber composed of a polycrystallinediamond and the diamond grains constituting the polycrystalline diamondof this scriber have an average grain diameter of 80 nm to 1 μm, whichis in the range defined by the present invention. However, as describedabove, a polycrystalline diamond produced by the production methoddescribed in Ref 1 (Ref 2) contains carbonate remaining after sintering.Therefore, such a polycrystalline diamond is different in structure froma polycrystalline diamond according to the present invention.

The inventors of the present invention produced scribers from diamondsobtained by the methods described in Refs. 5 to 7 above and inspectedthe workability of these scribers. This inspection revealed that, thediamonds obtained by the methods described in these References containcoarse grains as described above and hence portions corresponding tosuch coarse grains wear extremely rapidly.

The inventors have found that, to allow a desired stable working, suchportions wearing extremely rapidly needs to be eliminated, and this isachieved by controlling the distribution of the grain diameters of asinter. Accordingly, a scriber including a polycrystalline diamondhaving a controlled distribution of grain diameters according to thepresent invention was produced. Grains wearing extremely rapidly wereeliminated in this scriber and a desired stable working was achievedwith the scriber for a long period of time.

Polycrystalline diamond constituting a scriber preferably has a hardnessof 100 GPa or more. When the average grain diameter is 50 nm or less or2500 nm or more, the hardness becomes less than 100 GPa. When thehardness is less than 100 GPa, wearing away is caused in a short periodof time and hence stable working is not possible for a long period oftime and the scriber has a shorter life.

Hereinafter, a diamond cutting tool according to the present inventionwill be described in detail.

Since polycrystalline diamond serving as the material of a diamond toolaccording to the present invention is the above-describedpolycrystalline diamond according to the present invention, thepolycrystalline diamond substantially being a single-phase diamond(purity of 99% or more) and not containing a metal binder such ascobalt. For this reason, a diamond cutting tool according to the presentinvention does not wear unevenly, which does occur in diamond toolsincluding monocrystals.

The inventors of the present invention produced diamond tools fromdiamonds obtained by the methods described in Refs. 5 to 7 above andinspected the workability of these tools. This inspection revealed that,the diamonds obtained by the methods described in these Referencescontain coarse grains as described above and hence portionscorresponding to such coarse grains wear extremely rapidly. In thiscase, such portions cause streaky scratches or the like in metal beingworked and hence a desired working is not possible, which has been aproblem.

The inventors have found that, to allow a desired stable working, suchportions wearing extremely rapidly needs to be eliminated, and this isachieved by controlling the distribution of the grain diameters of asinter. Accordingly, a diamond tool including a polycrystalline diamondhaving a controlled distribution of grain diameters according to thepresent invention was produced. Grains wearing extremely rapidly wereeliminated in this tool and a desired stable working was achieved withthe tool for a long period of time.

Polycrystalline diamond constituting a diamond cutting tool preferablyhas a hardness of 100 GPa or more. When the polycrystalline diamond hasa hardness of less than 100 GPa, wearing away is caused in a shortperiod of time and hence stable working is not possible for a longperiod of time and such a diamond tool has a shorter life.

For this reason, the sintered grains of polycrystalline diamond are madeto have an average grain diameter of more than 50 nm and less than 2500nm and a hardness of 100 GPa or more. When the average grain diameter is50 nm or less or 2500 nm or more, the hardness becomes less than 100GPa.

The grains of a sinter are made to have a D90 grain diameter of (averagegrain diameter+0.9×average grain diameter) or less to suppress abnormalwearing.

Hereinafter, a scribing wheel according to the present invention will bedescribed in detail.

Since polycrystalline diamond serving as the material of a scribingwheel according to the present invention is the above-describedpolycrystalline diamond according to the present invention, thepolycrystalline diamond substantially being a single-phase diamond(purity of 99% or more) and not containing a metal binder such ascobalt. For this reason, a scribing wheel according to the presentinvention does not wear unevenly, which does occur in scribing wheelsincluding monocrystals.

The inventors of the present invention produced scribing wheels frompolycrystalline diamonds obtained by the methods described in Refs. 5 to7 above and inspected the workability of these scribing wheels. Thisinspection revealed that, the diamonds obtained by the methods describedin these References contain coarse grains as described above and henceportions corresponding to such coarse grains wear extremely rapidly.

The inventors have found that, to allow a desired stable working, suchportions wearing extremely rapidly needs to be eliminated, and this isachieved by controlling the distribution of the grain diameters of asinter. Accordingly, a scribing wheel including a polycrystallinediamond having a controlled distribution of grain diameters according tothe present invention was produced. Grains wearing extremely rapidlywere eliminated in this scribing wheel and a desired stable working wasachieved with the scribing wheel for a long period of time.

Polycrystalline diamond constituting a scribing wheel preferably has ahardness of 100 GPa or more. When the average grain diameter is 50 nm orless or 2500 nm or more, the hardness becomes less than 100 GPa. Whenthe hardness is less than 100 GPa, wearing away is caused in a shortperiod of time and hence stable working is not achieved for a longperiod of time and the scribing wheel has a shorter life.

Examples

Hereinafter, the present invention is described with reference toexamples in which polycrystalline diamond according to the presentinvention is used as materials for water jet orifices, styluses forgravure printing, scribers, diamond cutting tools, and scribing wheels.

Measurement methods and evaluation methods used in Examples andComparative Examples will be described.

<Average Grain Diameter and D90 Grain Diameter>

The D50 grain diameters (average grain diameters) and the D90 graindiameters of graphite grains in fired graphite material and sintereddiamond grains in polycrystalline diamond in the present invention areobtained by conducting image analysis on the basis of photographicimages with a transmission electron microscope under a magnification of100,000 to 500,000.

Hereinafter, this method is described in detail.

First, the distribution of the diameters of crystal grains constitutinga sinter is determined on the basis of an image taken with atransmission electron microscope. Specifically, each grain is sampled, asampled grain is subjected to binarization, and the area (S) of eachgrain is calculated with an image analysis software (for example, ScionImage manufactured by Scion Corporation). The diameter (D) of each grainis calculated as the diameter (D=2√(S/π)) of a circle having the samearea as the grain.

Second, the thus-obtained distribution of grain diameters is processedwith a data analysis software (for example, Origin manufactured byOriginLab Corporation, Mathchad manufactured by Parametric TechnologyCorporation, or the like) to calculate the D50 grain diameter and theD90 grain diameter.

A transmission electron microscope used in Examples and ComparativeExamples described below was an H-9000 manufactured by Hitachi, Ltd.

<Hardness>

Hardness was measured in Examples and Comparative Examples with a Knoopindenter with a measurement load of 4.9 N.

<Surface Roughness>

The surface roughness of the interior surface of an orifice bore wasadjusted by adjusting the particle diameters of a polishing agent forpolishing the interior surface. Surface roughness was measured inaccordance with JIS B0601 with a contact-type surface roughness tester.Since a measurement stylus cannot be inserted into an orifice bore,another orifice separately produced by the same processes was cut andmeasured.

Example 1 Water Jet Orifice

Examples of orifices according to embodiments of the present inventionare described below.

Examples 1-1 to 1-3 are examples in which surface roughness was varied.Examples 1-4 to 1-6 are examples in which orifice bore diameter wasvaried. Examples 1-7 to 1-12 are examples in which average graindiameter and D90 grain diameter were varied. Examples 1-13 and 1-14 areexamples in which both average grain diameter and orifice bore diameterwere increased.

Example 1-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 370 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 110 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of200 μm, an orifice level of 5 mm, and a surface roughness Ra of 290 nmin the surface of the orifice bore. This orifice was evaluated for awater jet cutting property. The cutting time over which the orificediameter was expanded to 300 μm was determined and it was a long time of160 hours. For comparison purposes, an orifice composed of a sintereddiamond having an average crystal grain diameter of 5 μm (containing acobalt binder) was also evaluated for the same cutting property and thetime was about 50 hours, which were extremely short.

Example 1-2

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 370 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 110 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of200 μm, an orifice level of 5 mm, and a surface roughness Ra of 50 nm inthe surface of the orifice bore. This orifice was evaluated for a waterjet cutting property. The cutting time over which the orifice diameterwas expanded to 300 μm was determined and it was a long time of 240hours. For comparison purposes, an orifice composed of a sintereddiamond having an average crystal grain diameter of 5 μm (containing acobalt binder) was also evaluated for the same cutting property and thetime was about 70 hours, which were extremely short.

Example 1-3

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 370 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 110 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of200 μm, an orifice level of 5 mm, and a surface roughness Ra of 5 nm inthe surface of the orifice bore. This orifice was evaluated for a waterjet cutting property. The cutting time over which the orifice diameterwas expanded to 300 μm was determined and it was a long time of 520hours. For comparison purposes, an orifice composed of a sintereddiamond having an average crystal grain diameter of 5 μm (containing acobalt binder) was also evaluated for the same cutting property and thetime was about 90 hours, which were extremely short.

Example 1-4

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter), was prepared as non-diamond carbon serving as the material ofdiamond. This material was directly converted and sintered into diamondunder a pressure condition under which diamond is thermodynamicallystable. As a result, a polycrystalline diamond having an average graindiameter of 200 nm and a D90 grain diameter of 370 nm was obtained. Thethus-obtained polycrystalline diamond had an extremely high hardness of110 GPa. An orifice was produced from this polycrystalline material, theorifice having an orifice bore diameter of 450 μm, an orifice level of 5mm, and a surface roughness Ra of 290 nm in the surface of the orificebore. This orifice was evaluated for a water jet cutting property. Thecutting time over which the orifice diameter was expanded to 550 μm wasdetermined and it was a long time of 165 hours. For comparison purposes,an orifice composed of a sintered diamond having an average crystalgrain diameter of 5 μm (containing a cobalt binder) was also evaluatedfor the same cutting property and the time was about 55 hours, whichwere extremely short.

Example 1-5

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 370 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 110 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of50 μm, an orifice level of 5 mm, and a surface roughness Ra of 290 nm inthe surface of the orifice bore. This orifice was evaluated for a waterjet cutting property. The cutting time over which the orifice diameterwas expanded to 100 μm was determined and it was a long time of 210hours. For comparison purposes, an orifice composed of a sintereddiamond having an average crystal grain diameter of 5 μm (containing acobalt binder) was also evaluated for the same cutting property and thetime was about 75 hours, which were extremely short.

Example 1-6

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 370 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 110 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of15 μm, an orifice level of 7 mm, and a surface roughness Ra of 290 nm inthe surface of the orifice bore. This orifice was evaluated for a waterjet cutting property. The cutting time over which the orifice diameterwas expanded to 30 μm was determined and it was a long time of 230hours. For comparison purposes, an orifice composed of a sintereddiamond having an average crystal grain diameter of 5 μm (containing acobalt binder) was also evaluated for the same cutting property and thetime was about 80 hours, which were extremely short.

Example 1-7

Graphite having an average grain diameter of 110 nm and a D90 graindiameter of 175 nm, which is (average grain diameter+0.7×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 230 nm and a D90 grain diameter of 380 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 115 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of200 μm, an orifice level of 5 mm, and a surface roughness Ra of 280 nmin the surface of the orifice bore. This orifice was evaluated for awater jet cutting property. The cutting time over which the orificediameter was expanded to 300 μm was determined and it was a long time of180 hours.

Example 1-8

Graphite having an average grain diameter of 95 nm and a D90 graindiameter of 135 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 180 nm and a D90 grain diameter of 260 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 125 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of200 μm, an orifice level of 5 mm, and a surface roughness Ra of 280 nmin the surface of the orifice bore. This orifice was evaluated for awater jet cutting property. The cutting time over which the orificediameter was expanded to 300 μm was determined and it was a long time of210 hours.

Example 1-9

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 55 nm and a D90 grain diameter of 80 nm wasobtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 105 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of200 μm, an orifice level of 5 mm, and a surface roughness Ra of 250 nmin the surface of the orifice bore. This orifice was evaluated for awater jet cutting property. The cutting time over which the orificediameter was expanded to 200 μm was determined and it was a long time of130 hours.

Example 1-10

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 9 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 560 nm anda D90 grain diameter of 830 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 120 GPa. Anorifice was produced from this polycrystalline material, the orificehaving an orifice bore diameter of 200 μm, an orifice level of 5 mm, anda surface roughness Ra of 240 nm in the surface of the orifice bore.This orifice was evaluated for a water jet cutting property. The cuttingtime over which the orifice diameter was expanded to 300 μm wasdetermined and it was a long time of 160 hours.

Example 1-11

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 9 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 1100 nmand a D90 grain diameter of 1600 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 112 GPa. Anorifice was produced from this polycrystalline material, the orificehaving an orifice bore diameter of 200 μm, an orifice level of 5 mm, anda surface roughness Ra of 250 nm in the surface of the orifice bore.This orifice was evaluated for a water jet cutting property. The cuttingtime over which the orifice diameter was expanded to 300 μm wasdetermined and it was a long time of 150 hours.

Example 1-12

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 9 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 2400 nmand a D90 grain diameter of 3500 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 102 GPa. Anorifice was produced from this polycrystalline material, the orificehaving an orifice bore diameter of 200 μm, an orifice level of 5 mm, anda surface roughness Ra of 270 nm in the surface of the orifice bore.This orifice was evaluated for a water jet cutting property. The cuttingtime over which the orifice diameter was expanded to 300 μm wasdetermined and it was a long time of 110 hours.

Example 1-13

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 9 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 2400 nmand a D90 grain diameter of 3500 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 102 GPa. Anorifice was produced from this polycrystalline material, the orificehaving an orifice bore diameter of 1500 μm, an orifice level of 5 mm,and a surface roughness Ra of 270 nm in the surface of the orifice bore.This orifice was evaluated for a water jet cutting property. The cuttingtime over which the orifice diameter was expanded to 2000 μm wasdetermined and it was a long time of 210 hours.

Example 1-14

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 9 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 2400 nmand a D90 grain diameter of 3500 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 102 GPa. Anorifice was produced from this polycrystalline material, the orificehaving an orifice bore diameter of 3500 μm, an orifice level of 0.7 mm,and a surface roughness Ra of 270 nm in the surface of the orifice bore.This orifice was evaluated for a water jet cutting property. The cuttingtime over which the orifice diameter was expanded to 4500 μm wasdetermined and it was a long time of 160 hours.

Comparative Example 1-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 370 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 110 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of200 μm, an orifice level of 5 mm, and a surface roughness Ra of 350 nmin the surface of the orifice bore. This orifice was evaluated for awater jet cutting property. The cutting time over which the orificediameter was expanded to 300 μm was determined and it was a short timeof 95 hours.

Comparative Example 1-2

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 210 nm, which is about (average grain diameter+1.1×averagegrain diameter), was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 400 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 112 GPa. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of200 μm, an orifice level of 5 mm, and a surface roughness Ra of 290 nmin the surface of the orifice bore. This orifice was evaluated for awater jet cutting property. The cutting time over which the orificediameter was expanded to 300 μm was determined and it was a short timeof 90 hours.

Comparative Example 1-3

Graphite having an average grain diameter of 20 nm and a D90 graindiameter of 37 nm, which is about (average grain diameter+0.9×averagegrain diameter), was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 45 nm and a D90 grain diameter of 80 nm wasobtained. The thus-obtained polycrystalline diamond had a hardness of 95GPa and was slightly soft. An orifice was produced from thispolycrystalline material, the orifice having an orifice bore diameter of200 μm, an orifice level of 5 mm, and a surface roughness Ra of 250 nmin the surface of the orifice bore. This orifice was evaluated for awater jet cutting property. The cutting time over which the orificediameter was expanded to 300 μm was determined and it was a short timeof 80 hours.

Comparative Example 1-4

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is about (average grain diameter+0.9×averagegrain diameter), was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable over a long period of time. As a result, apolycrystalline diamond having an average grain diameter of 2700 nm anda D90 grain diameter of 3900 nm was obtained. The thus-obtainedpolycrystalline diamond had a hardness of 91 GPa and was slightly soft.An orifice was produced from this polycrystalline material, the orificehaving an orifice bore diameter of 200 μm, an orifice level of 5 mm, anda surface roughness Ra of 240 nm in the surface of the orifice bore.This orifice was evaluated for a water jet cutting property. The cuttingtime over which the orifice diameter was expanded to 300 μm wasdetermined and it was a short time of 85 hours.

Table I shows values of the sintered grains of the polycrystallinediamonds in Examples and Comparative Examples above in terms of averagegrain diameter, D90 grain diameter, a coefficient (K), hardness, andwear life. Note that the coefficient (K) is defined by Equation (1)below.

D90 grain diameter=average grain diameter+average grain diameter×K   (1)

TABLE I Orifice Average bore Orifice Life of grain Surface diameterlevel Life Co-containing diameter D90 Hardness roughness (D) (L) hourdiamond hour (nm) (nm) Coefficient (GPa) (nm) (μm) (mm) L/D*¹⁾ (H) (H)Example 1-1 200 370 0.85 110 290 200 5 25 160 50 Example 1-2 200 3700.85 110 50 200 5 25 240 70 Example 1-3 200 370 0.85 110 5 200 5 25 52090 Example 1-4 200 370 0.85 110 290 450 5 11 165 55 Example 1-5 200 3700.85 110 290 50 5 100 210 75 Example 1-6 200 370 0.85 110 290 15 7 467230 80 Example 1-7 230 380 0.65 115 280 200 5 25 180 — Example 1-8 180260 0.44 125 280 200 5 25 210 — Example 1-9 55 80 0.45 105 250 200 5 25130 — Example 1-10 560 830 0.48 120 240 200 5 25 160 — Example 1-11 11001600 0.45 112 250 200 5 25 150 — Example 1-12 2400 3500 0.46 102 270 2005 25 110 — Example 1-13 2400 3500 0.46 102 270 1500 5 3 210 — Example1-14 2400 3500 0.46 102 270 3500 0.7 0.2 160 — Comparative 200 370 0.85110 350 200 5 25 95 — Example 1-1 Comparative 200 400 1.00 112 290 200 525 90 — Example 1-2 Comparative 45 80 0.78 95 250 200 5 25 80 — Example1-3 Comparative 2700 3900 0.44 91 240 200 5 25 85 — Example 1-4 *¹⁾L/D =orifice bore diameter (D)/orifice level (L)

Example 2 Stylus for Gravure Printing

Examples of styluses for gravure printing according to the presentinvention and Comparative Examples are described below.

An evaluation method for styluses in terms of wear resistance will bedescribed.

<Evaluation of Wear Resistance>

A stylus having an included angle of 120° was produced frompolycrystalline diamond obtained. A copper workpiece was worked withthis stylus being driven at a frequency of 8 kHz and working time overwhich wear depth in an edge line portion on one side was increased to 10μm was determined The wear resistance of the stylus was evaluated on thebasis of this working time defined as the wear life of the stylus.

Example 2-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 370 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 110 GPa. A stylus produced from this polycrystallinediamond had a long wear life of 240 hours. For comparison purposes, astylus composed of monocrystalline diamond was evaluated for the sameworking property and the time was about 60 hours, which were extremelyshort.

Example 2-2

Graphite having an average grain diameter of 110 nm and a D90 graindiameter of 175 nm, which is (average grain diameter+0.7×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 230 nm and a D90 grain diameter of 380 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 115 GPa. A stylus produced from this polycrystallinediamond had a long wear life of 280 hours.

Example 2-3

Graphite having an average grain diameter of 95 nm and a D90 graindiameter of 135 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 180 nm and a D90 grain diameter of 260 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 125 GPa. A stylus produced from this polycrystallinediamond had a long wear life of 320 hours.

Example 2-4

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 55 nm and a D90 grain diameter of 80 nm wasobtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 105 GPa. A stylus having an included angle of 120° wasproduced from the obtained polycrystalline diamond. This stylus producedfrom the polycrystalline diamond had a long wear life of 200 hours.

Example 2-5

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 4 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 560 nm anda D90 grain diameter of 830 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 120 GPa. Astylus produced from this polycrystalline diamond had a long wear lifeof 180 hours.

Example 2-6

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 5 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 1100 nmand a D90 grain diameter of 1600 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 112 GPa. Astylus produced from this polycrystalline diamond had a long wear lifeof 170 hours.

Example 2-7

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 6 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 2400 nmand a D90 grain diameter of 3500 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 102 GPa. Astylus produced from this polycrystalline diamond had a long wear lifeof 150 hours.

Comparative Example 2-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 210 nm, which is (average grain diameter+1.1×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 400 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 112 GPa. A stylus produced from this polycrystallinediamond had a short wear life of 90 hours.

Comparative Example 2-2

Graphite having an average grain diameter of 20 nm and a D90 graindiameter of 37 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 45 nm and a D90 grain diameter of 80 nm wasobtained. The thus-obtained polycrystalline diamond had a hardness of 95GPa and was slightly soft. A stylus produced from this polycrystallinediamond had a short wear life of 85 hours.

Comparative Example 2-3

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 2700 nm and a D90 grain diameter of 3900 nmwas obtained. The thus-obtained polycrystalline diamond had a hardnessof 91 GPa and was slightly soft. A stylus produced from thispolycrystalline diamond had a short wear life of 70 hours.

Comparative Example 2-4

A stylus produced from monocrystalline diamond serving as a material wastested for wear resistance in the same manner as in Example 1 and thisstylus had a wear life of 60 hours.

Table II shows values of the sintered grains of the polycrystallinediamonds in Examples and Comparative Examples above in terms of averagegrain diameter, D90 grain diameter, the coefficient (K), hardness, andwear life. Note that the coefficient (K) is defined by Eq. (1) above.

TABLE II Average grain diameter Coefficient Hardness Wear life nm D90 nm(K) GPa hour (H) Example 2-1 200 370 0.85 110 240 Example 2-2 230 3800.65 115 280 Example 2-3 180 260 0.44 125 320 Example 2-4 55 80 0.45 105200 Example 2-5 560 830 0.48 120 180 Example 2-6 1100 1600 0.45 112 170Example 2-7 2400 3500 0.46 102 150 Comparative 200 400 1.00 112 90Example 2-1 Comparative 45 80 0.78 95 85 Example 2-2 Comparative 27003900 0.44 91 70 Example 2-3 Comparative — — — — 60 Example 2-4

Example 3 Scriber

Examples of scribers according to the present invention and ComparativeExamples are described below.

An evaluation method for scribers in terms of wear resistance will bedescribed.

<Evaluation of Wear Resistance>

A 4-point scriber was produced from polycrystalline material obtainedand it was subjected to a wear test where a sapphire substrate wasscribed with the scriber under a load of 50 g, at a scribing speed of 1cm/min, and for a scribing distance of 1 m. The wear resistance of thescriber was evaluated on the basis of abrasion loss in the test.

Example 3-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 370 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 110 GPa. An abrasion loss of a scriber produced fromthis polycrystalline diamond was extremely small and it was about 1/70of that of a scriber composed of monocrystalline diamond.

Example 3-2

Graphite having an average grain diameter of 110 nm and a D90 graindiameter of 175 nm, which is (average grain diameter+0.7×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 230 nm and a D90 grain diameter of 380 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 115 GPa. An abrasion loss of a scriber produced fromthis polycrystalline diamond was extremely small and it was about 1/80of that of a scriber composed of monocrystalline diamond.

Example 3-3

Graphite having an average grain diameter of 95 nm and a D90 graindiameter of 135 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 180 nm and a D90 grain diameter of 260 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 125 GPa. An abrasion loss of a scriber produced fromthis polycrystalline diamond was extremely small and it was about 1/90of that of a scriber composed of monocrystalline diamond.

Example 3-4

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 55 nm and a D90 grain diameter of 80 nm wasobtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 105 GPa. An abrasion loss of a scriber produced fromthis polycrystalline diamond was extremely small and it was about 1/60of that of a scriber composed of monocrystalline diamond.

Example 3-5

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 4 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 560 nm anda D90 grain diameter of 830 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 120 GPa. Anabrasion loss of a scriber produced from this polycrystalline diamondwas extremely small and it was about 1/50 of that of a scriber composedof monocrystalline diamond.

Example 3-6

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 5 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 1100 nmand a D90 grain diameter of 1600 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 112 GPa. Anabrasion loss of a scriber produced from this polycrystalline diamondwas extremely small and it was about 1/50 of that of a scriber composedof monocrystalline diamond.

Example 3-7

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 6 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 2400 nmand a D90 grain diameter of 3500 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 102 GPa. Anabrasion loss of a scriber produced from this polycrystalline diamondwas extremely small and it was about 1/40 of that of a scriber composedof monocrystalline diamond.

Comparative Example 3-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 210 nm, which is (average grain diameter+1.1×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 400 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 112 GPa. An abrasion loss of a scriber produced fromthis polycrystalline diamond was about ¼ of that of a scriber composedof monocrystalline diamond.

Comparative Example 3-2

Graphite having an average grain diameter of 20 nm and a D90 graindiameter of 37 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 45 nm and a D90 grain diameter of 80 nm wasobtained. The thus-obtained polycrystalline diamond had a hardness of 95GPa and was slightly soft. An abrasion loss of a scriber produced fromthis polycrystalline diamond was about ⅓ of that of a scriber composedof monocrystalline diamond.

Comparative Example 3-3

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 2700 nm and a D90 grain diameter of 3900 nmwas obtained. The thus-obtained polycrystalline diamond had a hardnessof 91 GPa and was slightly soft. An abrasion loss of a scriber producedfrom this polycrystalline diamond was about ½ of that of a scribercomposed of monocrystalline diamond.

Table III shows values of the sintered grains of the polycrystallinediamonds in Examples and Comparative Examples above in terms of averagegrain diameter, D90 grain diameter, the coefficient (K), hardness, andabrasion loss. Note that the coefficient (K) is defined by Eq. (1)above.

TABLE III Average Abrasion loss grain Co- Ratio relative diameter D90efficient Hardness to monocrystal [nm] [nm] (K) [Gpa] (reciprocal)Example 3-1 200 370 0.85 110 68.0 Example 3-2 230 380 0.65 115 79.3Example 3-3 180 260 0.44 125 90.7 Example 3-4 55 80 0.45 105 56.7Example 3-5 560 830 0.48 120 51.0 Example 3-6 1100 1600 0.45 112 48.2Example 3-7 2400 3500 0.46 102 42.5 Comparative 200 400 1.00 112 3.6Example 3-1 Comparative 45 80 0.78 95 3.4 Example 3-2 Comparative 27003900 0.44 91 2.8 Example 3-3

Example 4 Diamond Cutting Tool

Examples of diamond cutting tools according to embodiments of thepresent invention are described below.

An evaluation method for diamond cutting tools in terms of wearresistance will be described.

<Wear Resistance (Tool Life)>

Cutting tools having an edge included angle of 90° and an edge R of 100nm were produced from polycrystalline diamonds obtained in Examples andComparative Examples and these cutting tools were used to form grooveshaving a depth of 5 μm and a pitch of 5 μm in a metal plate that was acopper plate on which nickel was plated. The wear resistance of thecutting tools was evaluated on the basis of time (tool life) over whichthe edges of the cutting tools wore down to about 1 μm.

Example 4-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 370 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 110 GPa. A cutting tool produced from thispolycrystalline diamond had an extremely long tool life of 15 hours.

Example 4-2

Graphite having an average grain diameter of 110 nm and a D90 graindiameter of 175 nm, which is (average grain diameter+0.7×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 230 nm and a D90 grain diameter of 380 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 115 GPa. A cutting tool produced from thispolycrystalline diamond had an extremely long tool life of 18 hours.

Example 4-3

Graphite having an average grain diameter of 95 nm and a D90 graindiameter of 135 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 180 nm and a D90 grain diameter of 260 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 125 GPa. A cutting tool produced from thispolycrystalline diamond had an extremely long tool life of 20 hours.

Example 4-4

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 55 nm and a D90 grain diameter of 80 nm wasobtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 105 GPa. A cutting tool produced from thispolycrystalline diamond had an extremely long tool life of 13 hours.

Example 4-5

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 4 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 560 nm anda D90 grain diameter of 830 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 120 GPa. Acutting tool produced from this polycrystalline diamond had an extremelylong tool life of 11 hours.

Example 4-6

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 5 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 1100 nmand a D90 grain diameter of 1600 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 112 GPa. Acutting tool produced from this polycrystalline diamond had an extremelylong tool life of 10 hours.

Example 4-7

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond over a longer time than in Example 6 under a pressurecondition under which diamond is thermodynamically stable. As a result,a polycrystalline diamond having an average grain diameter of 2400 nmand a D90 grain diameter of 3500 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 102 GPa. Acutting tool produced from this polycrystalline diamond had an extremelylong tool life of 9 hours.

Comparative Example 4-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 210 nm, which is (average grain diameter+1.1×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 200 nm and a D90 grain diameter of 400 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 112 GPa. A cutting tool produced from thispolycrystalline diamond had a tool life of 6 hours.

Comparative Example 4-2

Graphite having an average grain diameter of 20 nm and a D90 graindiameter of 37 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 45 nm and a D90 grain diameter of 80 nm wasobtained. The thus-obtained polycrystalline diamond had a hardness of 95GPa and was slightly soft. A cutting tool produced from thispolycrystalline diamond had a tool life of 5 hours.

Comparative Example 4-3

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as non-diamond carbon serving as thematerial of diamond. This material was directly converted and sinteredinto diamond under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 2700 nm and a D90 grain diameter of 3900 nmwas obtained. The thus-obtained polycrystalline diamond had a hardnessof 91 GPa and was slightly soft. A cutting tool produced from thispolycrystalline diamond had a tool life of 4 hours.

Comparative Example 4-4

A tool produced from monocrystalline diamond serving as a material wastested for wear resistance in the same manner as in Example 1 and thistool had a tool life of 3 hours.

Table IV shows the values of the sintered grains of the polycrystallinediamonds in Examples and Comparative Examples above in terms of averagegrain diameter, D90 grain diameter, the coefficient (K), hardness, andtool life. Note that the coefficient (K) is defined by Eq. (1) above.

TABLE IV Average grain D90 grain Co- diameter diameter efficientHardness Tool life [nm] [nm] (K) [Gpa] [Hr] Example 4-1 200 370 0.85 11015 Example 4-2 230 380 0.65 115 18 Example 4-3 180 260 0.44 125 20Example 4-4 55 80 0.45 105 13 Example 4-5 560 830 0.48 120 11 Example4-6 1100 1600 0.45 112 10 Example 4-7 2400 3500 0.46 102 9 Comparative200 400 1.00 112 6 Example 4-1 Comparative 45 80 0.78 95 5 Example 4-2Comparative 2700 3900 0.44 91 4 Example 4-3 Comparative — — — — 3Example 4-4

Example 5 Scribing Wheel

Examples of scribing wheels according to embodiments of the presentinvention are described below.

An evaluation method for scribing wheels in terms of a scribing propertywill be described.

<Evaluation of Scribing Property>

Scribing wheels having a diameter of 3 mm, a thickness of 0.8 mm, and anedge included angle of 120° were produced from polycrystalline diamondsobtained in Examples and Comparative Examples. These scribing wheelswere used to scribe glass substrates and the scribing property of thescribing wheels was evaluated by determining scribed distances.

Example 5-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond under apressure condition under which diamond is thermodynamically stable. As aresult, a polycrystalline diamond having an average grain diameter of200 nm and a D90 grain diameter of 370 nm was obtained. Thethus-obtained polycrystalline diamond had an extremely high hardness of110 GPa. The resultant polycrystalline material was evaluated in termsof scribing. As a result, scribing for a long distance of about 300 kmwas achieved with this polycrystalline diamond.

Example 5-2

Graphite having an average grain diameter of 110 nm and a D90 graindiameter of 175 nm, which is (average grain diameter+0.7×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond under apressure condition under which diamond is thermodynamically stable. As aresult, a polycrystalline diamond having an average grain diameter of230 nm and a D90 grain diameter of 380 nm was obtained. Thethus-obtained polycrystalline diamond had an extremely high hardness of115 GPa. The resultant polycrystalline material was evaluated in termsof scribing. As a result, scribing for a long distance of about 350 kmwas achieved with this polycrystalline diamond.

Example 5-3

Graphite having an average grain diameter of 95 nm and a D90 graindiameter of 135 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond under apressure condition under which diamond is thermodynamically stable. As aresult, a polycrystalline diamond having an average grain diameter of180 nm and a D90 grain diameter of 260 nm was obtained. Thethus-obtained polycrystalline diamond had an extremely high hardness of125 GPa. The resultant polycrystalline material was evaluated in termsof scribing. As a result, scribing for a long distance of about 400 kmwas achieved with this polycrystalline diamond.

Example 5-4

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond under apressure condition under which diamond is thermodynamically stable. As aresult, a polycrystalline diamond having an average grain diameter of 55nm and a D90 grain diameter of 80 nm was obtained. The thus-obtainedpolycrystalline diamond had an extremely high hardness of 105 GPa. Theresultant polycrystalline material was evaluated in terms of scribing.As a result, scribing for a long distance of about 250 km was achievedwith this polycrystalline diamond.

Example 5-5

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond over a longertime than in Example 4 under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 560 nm and a D90 grain diameter of 830 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 120 GPa. The resultant polycrystalline material wasevaluated in terms of scribing. As a result, scribing for a longdistance of about 230 km was achieved with this polycrystalline diamond.

Example 5-6

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond over a longertime than in Example 5 under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 1100 nm and a D90 grain diameter of 1600 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 112 GPa. The resultant polycrystalline material wasevaluated in terms of scribing. As a result, scribing for a longdistance of about 210 km was achieved with this polycrystalline diamond.

Example 5-7

Graphite having an average grain diameter of 30 nm and a D90 graindiameter of 40 nm, which is (average grain diameter+0.5×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond over a longertime than in Example 6 under a pressure condition under which diamond isthermodynamically stable. As a result, a polycrystalline diamond havingan average grain diameter of 2400 nm and a D90 grain diameter of 3500 nmwas obtained. The thus-obtained polycrystalline diamond had an extremelyhigh hardness of 102 GPa. The resultant polycrystalline material wasevaluated in terms of scribing. As a result, scribing for a longdistance of about 190 km was achieved with this polycrystalline diamond.

Comparative Example 5-1

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 210 nm, which is (average grain diameter+1.1×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond under apressure condition under which diamond is thermodynamically stable. As aresult, a polycrystalline diamond having an average grain diameter of200 nm and a D90 grain diameter of 400 nm was obtained. Thethus-obtained polycrystalline diamond had an extremely high hardness of112 GPa. The resultant polycrystalline material was evaluated in termsof scribing. As a result, scribing for a short distance of about 120 kmwas barely conducted with this polycrystalline diamond.

Comparative Example 5-2

Graphite having an average grain diameter of 20 nm and a D90 graindiameter of 37 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond under apressure condition under which diamond is thermodynamically stable. As aresult, a polycrystalline diamond having an average grain diameter of 45nm and a D90 grain diameter of 80 nm was obtained. The thus-obtainedpolycrystalline diamond had a hardness of 95 GPa and was slightly soft.The resultant polycrystalline material was evaluated in terms ofscribing. As a result, scribing for a short distance of about 110 km wasbarely conducted with this polycrystalline diamond.

Comparative Example 5-3

Graphite having an average grain diameter of 100 nm and a D90 graindiameter of 180 nm, which is (average grain diameter+0.9×average graindiameter) or less, was prepared as the material of diamond. Thismaterial was directly converted and sintered into diamond under apressure condition under which diamond is thermodynamically stable. As aresult, a polycrystalline diamond having an average grain diameter of2700 nm and a D90 grain diameter of 3900 nm was obtained. The resultantpolycrystalline material was evaluated in terms of scribing. As aresult, scribing for a short distance of about 90 km was barelyconducted with this polycrystalline diamond.

Comparative Example 5-4

A scribing wheel was produced from monocrystalline diamond and evaluatedin terms of scribing. As a result, scribing for a short distance of 100km was barely conducted with this monocrystalline diamond.

Comparative Example 5-5

A scribing wheel was produced from a sintered diamond compact bound withmetal and evaluated in terms of scribing. As a result, scribing for ashort distance of 6 km was barely conducted with this sintered diamondcompact.

Table V shows values of the sintered grains of the polycrystallinediamonds in Examples and Comparative Examples above in terms of averagegrain diameter, D90 grain diameter, the coefficient, hardness, and toollife. Note that the coefficient (K) is defined by Eq. (1) above.

TABLE V Average grain Scribed diameter D90 Coefficient Hardness distance[nm] [nm] (K) [Gpa] [km] Example 5-1 200 370 0.85 110 300 Example 5-2230 380 0.65 115 350 Example 5-3 180 260 0.44 125 400 Example 5-4 55 800.45 105 250 Example 5-5 560 830 0.48 120 230 Example 5-6 1100 1600 0.45112 210 Example 5-7 2400 3500 0.46 102 190 Comparative 200 400 1.00 112120 Example 5-1 Comparative 45 80 0.78 95 110 Example 5-2 Comparative2700 3900 0.44 91 90 Example 5-3 Comparative — — — — 100 Example 5-4Comparative — — — — 6 Example 5-5

INDUSTRIAL APPLICABILITY

Polycrystalline diamond used in the present invention is less prone towear unevenly and allows stable working for a long period of timecompared with conventional monocrystalline diamonds and sintered diamondcompacts containing metal binders. Therefore, such polycrystallinediamond can be suitably applied to water jet orifices, styluses forgravure printing, scribers, cutting tools, and scribing wheels.

A water jet orifice according to the present invention can provide acutting width with stability for a long period of time compared withconventional orifices and hence can be suitably used as an orifice for awater jet configured to expel fluid containing rigid particles (aluminaor the like) at a high pressure to thereby cut or work workpieces.

1. Polycrystalline diamond obtained by converting and sinteringnon-diamond carbon under an ultrahigh pressure and at a high temperaturewithout addition of a sintering aid or a catalyst, wherein sintereddiamond grains constituting the polycrystalline diamond have an averagegrain diameter of more than 50 nm and less than 2500 nm and a purity of99% or more, and the diamond has a D90 grain diameter of (average graindiameter+average grain diameter×0.9) or less.
 2. The polycrystallinediamond according to claim 1, wherein the sintered diamond grains have aD90 grain diameter of (average grain diameter+average graindiameter×0.7) or less.
 3. The polycrystalline diamond according to claim1, wherein the sintered diamond grains have a D90 grain diameter of(average grain diameter+average grain diameter×0.5) or less.
 4. Thepolycrystalline diamond according to claim 1, wherein thepolycrystalline diamond has a hardness of 100 GPa or more.
 5. Thepolycrystalline diamond according to claim 1, wherein the non-diamondcarbon is a carbon material having a graphite-type layer structure.
 6. Awater jet orifice comprising the polycrystalline diamond according toclaim
 1. 7. The water jet orifice according to claim 6, wherein aninterior surface of an orifice bore through which water jet fluidpasses, the bore being formed in the polycrystalline diamond, has asurface roughness Ra of 300 nm or less.
 8. The water jet orificeaccording to claim 6, wherein the orifice bore formed in thepolycrystalline diamond has a diameter of 10 μm or more and 500 μm orless.
 9. The water jet orifice according to claim 6, wherein a ratio(L/D) of an orifice level (L) to an orifice bore diameter (D) is 10 to500, the orifice bore being formed in the polycrystalline diamond. 10.The water jet orifice according to claim 6, wherein the orifice boreformed in the polycrystalline diamond has a diameter of more than 500 μmand 5000 μm or less.
 11. The water jet orifice according to claim 6,wherein a ratio (L/D) of an orifice level (L) to an orifice borediameter (D) is 0.2 to 10, the orifice bore being formed in thepolycrystalline diamond.
 12. A stylus for gravure printing comprisingthe polycrystalline diamond according to claim
 1. 13. A scribercomprising the polycrystalline diamond according to claim
 1. 14. Thescriber according to claim 13, wherein a cutting face at a tip of thescriber has a shape of a polygon including three or more edges and theedges, in part or entirety, of the polygon are used as a blade.
 15. Adiamond cutting tool comprising the polycrystalline diamond according toclaim
 1. 16. A scribing wheel comprising the polycrystalline diamondaccording to claim 1.